1. Field of the Invention
The present invention relates to a method for optimizing link plates in a plate-link chain for use in a variable speed unit of a belt-driven conical-pulley transmission. The invention furthermore relates to a link plate configuration for such a plate-link chain.
2. Description of the Related Art
Belt-driven conical-pulley transmissions with continuously variable transmission ratios are used increasingly in modern motor vehicles, not only because of the driving comfort that can be achieved with them, but also for possible fuel consumption savings.
One component that is decisive for the durability and the torque transmission ability of the variable speed unit of such a belt-driven conical-pulley transmission is the endless torque-transmitting means itself, which can be designed as a plate-link chain, for example, as illustrated diagrammatically in FIG. 5 in a small section. Such a plate-link chain is composed of plate-links 10, which are connected with each other by means of rocker members 12. The plate-links 10 are arranged behind one another in several rows that extend in the direction of movement of the plate-link chain and that are arranged adjacent to each other. In FIG. 5 the plate 101 is part of the front row in the viewing direction, the plate 102 is part of a row adjacent to the front row, and plate 103 is part of another row. To connect the plates, rocker members 12 are provided, which extend through the respective plate openings 14 transversely to the direction of chain movement. In doing so, two rocker member pairs 161 and 162 extend through each plate opening, wherein the rocker members 121 and 122 are part of the rocker member pair 161 and the rocker members 123 and 124 are part of the rocker member pair 162. As can be seen, the exterior sides of the rocker members 121 and 124, which face away from each other, of the rocker member pairs 161 or 162 are supported on the inner surface of the plate opening 14, either on the front or the rear inner surface in relation to the direction of movement of the plate-link chain. The rocker members 122 and 123 that face each other are supported on the inner surfaces of plate openings of plates arranged in adjacent rows. The surfaces of the rocker members of each rocker member pair facing each other form rolling surfaces, on which the rocker members roll against each other when the radius R, at which the respective region of the plate-link chain is curved, changes.
Such a plate-link chain, as well as the corresponding variable speed unit with two conical disk pairs, around which the plate-link chain runs, are known as such and will therefore not be described in detail.
FIG. 6 shows a plate 10 and a rocker member 12 in an enlarged scale.
The plate 10 has two longitudinal legs 18 and two vertical legs 20, which jointly enclose the plate opening 14. According to FIG. 6, the rocker member 12, the rolling surface of which has been designated with the reference number 21, lies with its right side against the inner surface of the plate opening 14, wherein the contact surfaces have been adjusted with each other such that contact only occurs in the region of the transition between the longitudinal legs 18 to the vertical legs 20, and that in the region of the center of the vertical leg 20 no contact occurs between rocker member 20 and opening 14 of plate 10. When the plate 10 according to FIG. 6 is moved from right to left, forces are transmitted at the contact regions through the force transmitted by the plate-link chain, as represented in the figures with the arrows F indicating the load centers of the force and the force directions. Due to the offset design of the application points of the force in relation to the center of the longitudinal legs, tensile as well as bending stresses act within the longitudinal legs 18. Likewise, bending and tensile stresses act within the vertical legs 20.
Naturally, with given materials and given geometrical boundary conditions of the respective variable speed unit, i.e., its spacing, minimal and maximum revolution radius of the plate-link chain, etc., as well as the torque to be transmitted, the dimensions required for a plate depend upon the stresses that are active within the plate.
An object of the present invention is to design plates such that with given boundary conditions the plate is optimized with the goal of minimal material usage and hence minimal weight.